The aim of this project is to better understand the role of specific protein kinases in cell growth regulation, malignant transformation, and cellular resistance to chemotherapeutic drugs. Multidrug resistant MCF- 7/ADR cells exhibit elevated levels of a modified form of protein kinase C (PKC)-alpha. This altered form of PKC-alpha in the drug resistant MCF- 7/ADR cells was highly sensitive to oxidative inactivation when these cells were treated with hydrogen peroxide. In contrast, the PKC-alpha present in drug sensitive MCF-7/WT cells was not altered by hydrogen peroxide treatment. These results indicate that changes in the redox state of the cells, and thus in the oxidative modification of PKC-alpha, may play an important role in modulating the levels of PKC activity found in the drug sensitive versus drug resistant cells. Treatment of serum-deprived cortical astrocytes with low (subnanomolar) concentrations of vasoactive intestinal peptide (VIP) were observed to induce a significant increase in the level of PKC-alpha in the nuclear fraction. These data further suggest an important role for PKC in the transmission of signals from the plasma membrane to the nucleus, and indicate that very low concentrations of VIP apparently can act through a high affinity binding site which is coupled to a PKC-related signalling pathway. To better determine if the different isotypes of PKC might possess different regulatory properties within the cell, studies were carried out with stable transfectant NIH 3T3 cells which overexpress either PKC-delta or PKC-epsilon. Overproduction of either PKC isoform resulted in increased sodium-dependent phosphate uptake, but through apparently different mechanisms. These findings suggest that different PKC isozymes may act distinctly and specifically to regulate an in vivo cellular process. Previously, it was shown that the RI and Rll regulatory subunits of cAMP- dependent protein kinase (PKA) can be covalently modified by retinoylation. Results indicate that the RI and RII subunits also are retinoylated in human fibroblasts, and that the level of [3-H] RA labeling (retinoylation) of the RII subunit was greater in psoriatic fibroblasts than in normal fibroblasts. These results suggest that retinoylation may be involved, at least in part, in the reversal of the decreased levels of PKA activities observed when psoriatic cells are treated with RA.